Abstract

Very deep convection transports tropospheric air and water directly into the stratosphere. This transport may be underestimated by the general circulation models, due to their coarse resolution, limiting our capability to predict the future climate. The efficiency of this transport is analysed using a numerical simulation of the thunderstorm Hector the Convector. This simulation run with a resolution of 100 m and more than 1 billion grid points is a Giga Large-Eddy Simulation, the finest ever used for a case of very deep convection. It allows to represent the full Hector across the scales, from the mesoscale organisation to the most energetic eddies. The 200-km large thunderstorm is organised at the surface by the convergence lines. The latter appear along the sea breeze fronts and are intensified by the cold pools. The 10-km wide updrafts that overshoot into the stratosphere develop above these convergence lines and are characterized by a weak dilution. The km-scale eddies produce the irreversible mixing between the overshoots and the stratospheric air and finally the hydration. Sensitivity numerical experiments to the horizontal grid spacing show that a resolution of the order of 100 m is necessary for a reliable estimate of the hydration.